According to Yonhap News, around 6 pm on December 18, Jonghyun's older sister found Jonghyun unconscious at his home in Gangnam, Seoul. He was immediately rushed to the hospital, however, ultimately passed away.
Police suspect suicide as his sister has made reports around 4:42 pm, stating, "I think Jonghyun is about to commit suicide."
The police also stated that they've found a frying pan with brown liquid at Jonghyun's residence. It's assumed the unknown substance has led to his death.
Stay tuned for updates.
[UPDATE]: The brown liquid identified to be coal briquette. Jonghyun died from carbon monoxide poisoining.
If you or someone you know is at risk of self-harm or suicide, seek help as soon as possible by contacting agencies specializing in crisis intervention and suicide prevention in the United States and abroad.